​Project details

Access to the light station on Nootka Island was limited, requiring transport by helicopter and favourable weather conditions. This presented a challenge to the lighthouse keepers and coast guard operations throughout the year. As a result, Fisheries and Oceans Canada (DFO) sought to install a small craft dock to supplement operations. CWA was engaged to provide the design of water-connected elements including the abutments, the support system for the dock, and other associated details.

Challenges

The light station is situated in a cove that is in close proximity to territory historically occupied by the Nuu-cha-nulth people and has long been considered the location of the 1803 Boston shipwreck. As a result of the proximity to indigenous lands and the historical significance of the site, an archaeological investigation was required prior to the commencement of any construction. The investigation determined that any excavated soil and bedrock would need to be tested by an archaeologist to ensure it was free of any sensitive material. Additionally, pile driving could not be permitted on the seabed.

No climate, geotechnical, or other such information was available for Nootka Island, primarily as a result of the remote location of the site. However, an existing detailed survey of the site was available and provided to CWA.

Additional challenges resulted in the need for CWA to develop a new concept that satisfied the following conditions:

• The design would need to allow for continuous and unpredictable articulation of the float caused by wind and wave action
• The design would need to allow the float to be removed during winter months to minimize damage from storm activity
• The installation would need to be flexible with minimal volumes of concrete because of the difficulty of material delivery to the remote site
• Ground disturbance would need to be minimized to satisfy archaeological requirements

A pre-construction survey revealed inaccuracies in the original survey, including elevation discrepancies of approximately 2.5 metres and the presence of a large crevice in the location of the proposed abutment. As a result, CWA needed to produce a new solution with less than two weeks available before the start of construction.

Solutions

To meet the evolving challenges and requirements, CWA produced a total of four design concepts throughout the course of the project. The final design consisted of the following elements:

• A robust intermediate float that was designed to be permanently pinned to the truss and temporarily pinned to the seasonal float to allow removal of the timber float on a seasonal basis
• Gangways to bridge the space between the lighthouse and the floats over two spans
• A truss that fixed the float to the intermediate land-side abutment. Pinned connections allowed for articulation and the frame was made of hollow structural sections (HSS) to resist twisting action

The final design had very little environmental and archaeological impact. Furthermore, the design was flexible and allowed the contractor to install it wherever site conditions permitted.

In addition to the engineering design, CWA provided the following services:

• The implementation of planned procurement and construction sequencing to optimize the timing for installation, increase the quality of construction, and potentially reduce capital costs
• Procurement and tender technical support
• Construction field reviews